Among algae there are not only autotrophs, but also heterotrophs. How does this relate to adaptation processes?

Let us first recall that autotrophs are living organisms that are independently capable of creating organic matter. Heterotrophs use ready-made organic substances. All autotrophs are capable of photosynthesis. Some algae are heterotrophs because they cannot photosynthesize. This is due to a lack of sunlight (an essential component of photosynthesis). These algae are found deep under water, where sunlight does not enter. They are brown, not green.